This invention relates to microwave cooking and particularly to a container for microwave cooked foodstuffs which are to be provided with browned or crispened areas over at least a portion of their surfaces.
In the cooking of certain types of foodstuffs, such as potatoes, microwave ovens display a variety of advantages, the most common of which is rapidity of cooking. However, in certain other types of food products, such as French bread pizza, microwave cooking will usually not produce the desired browning. In order to provide such browning, a variety of package and container configurations have evolved in this art, such containers usually being provided with a microwave interactive substance or coating having the property of converting microwave energy to thermal energy. A microwave interactive material or substance is usually in the form of a coating that comprises part of the composition of the material from which the container is formed and has the property of increasing its own temperature by at least a partial absorption of the energy of the microwaves, and then transmitting thermal energy to a foodstuff. The usual frequency of such microwaves is about 2450 megahertz. A variety of microwave interactive materials has evolved, examples being shown in U.S. Pat. Nos. 2 830,162, issued to Copsol et al, 4,190,757 issued to Turpin et al, 4,283,427 issued to Winters et al 4,266,106 issued to Anderson et al. A widely used microwave interactive material is defined by a thin layer of aluminum, coated on a plastic film by vapor deposition techniques with the aluminum-coated film adhered to a paperboard substrate, and is shown in Seiferth U.S. Pat. No. 4,641,005.
While a variety of container configurations provided with a microwave interactive coating or substance are known, most of the containers suffer the drawback of not conforming to the food product which they package, this often being due to the irregular shape or size of the food product. This is particularly true when the food product is a solid item such as a French bread pizza that may vary in size and consequently may not conform exactly to a specified shape. This, in turn, will limit the effectiveness of the microwave interactive material in its browning function, because the interactive material will in such cases not be in direct contact with the food, even though the containers are of fairly uniform dimensions.